In numerous applications it is essential to reduce the manganese values in manganese ore to manganous oxide (MnO), and to recover the reduced ore in dry, stable form. Such ore reduction is generally carried out at temperatures in excess of 760.degree.C. (1400.degree.F.), normally at about 843.degree. to 954.degree.C. (1550.degree. to 1750.degree.F.). It is then necessary to cool the hot reduced ore, without reoxidation, to near room temperature, and desirably to less than 38.degree.C. (100.degree.F.).
Cooling of reduced ore has generally been accomplished in the presence of an inert gas, i.e., a gas which is non-oxidizing towards MnO. Even the most stable MnO has not been handled in a system open to the atmosphere unless it was first cooled to a temperature below about 120.degree.C. (248.degree.F.). This temperature reduction has generally been carried out either by indirect cooling in a kiln containing an inert or reducing atmosphere, or by forcing an inert gas through the reduced ore.
When reduced ore is introduced into an indirectly cooled kiln at 843.degree. to 954.degree.C. (1550.degree. to 1750.degree.F.), very rapid cooling takes place until the ore reaches a temperature of about 230.degree.C. (446.degree.F.). As the ore reaches this intermediate temperature, the rate of cooling becomes markedly slower. This is particularly true of ore which has a relatively coarse particle size. If the ore has been crushed rather than milled prior to reduction, kiln cooling is undesirably slow.